To take a stab at what he might mean by drifting, I will say that I think he might mean a rather unthinking habit of following the path that grown-ups set for us, be they parents, teachers or taste-makers, while choosing those things that we think (for complicated reasons perhaps unknown even to ourselves) we think we should choose, and then coming to the huge foggy void that meets us when we finish education.
As much as we love Brideshead Revisited, I think we should be told that this is no model for the undergraduate life. Waugh almost ruined his life by behaving like Charles and Sebastian. It wasn't their fashionable homoeroticism (which in Brideshead Revisited is worded very, very carefully indeed) as much as their drunkenness, their snobbery, and their contempt for work in general.
Charles and Sebastian and Waugh himself were serious drifters. After Oxford, Waugh drifted into teaching little boys, whom he loathed, and longed for his fashionable friends and wrote. He almost drowned himself. Fortunately for him, he wrote a book about people who drift, and it was a huge hit. Realizing he could make money through writing, Waugh ceased to drift quite so much.
In this he was like Charles, who discovered he could make a living through painting, although poor Charles does drift in and out of marriage and from country to country and from love to love, doesn't he? Poor Sebastian drifts in and out of sobriety and finally applies to a religious order. They are very nice men, but they can't take him on because he really doesn't have much to offer by then, poor man.
I read Brideshead Revisited at 11 or so, and as its homoeroticism went way over my head, as Waugh meant it to do, it became my second Bible. I fell in love with Sebastian, of course, so thank goodness this was in Canada, or I might have ended up like the young Nancy Mitford: longing to marry a charming, handsome aristocrat who mysteriously was not at all attracted to women.
I fell in love also with Oxford, which made any Canadian university a sad second choice, with literature, which--as everything I studied was written before 1950--gave me an unhealthy distaste for ordinary employment, and with aesthetic thrills:
Then we talked of [the wine] and nibbled Bath Oliver biscuits, and passed on to another wine; then back to the first, and on to the other, until all three were in circulation and the order of glasses got confused, and we fell out over which was which, and we passed the glasses to and fro between us until there were six glasses, some of them with mixed wines in them which we had filled from the wrong bottle, til we were obliged to start again with three clean glasses each, and the bottles were empty and our praise of them wilder and more exotic...
...And we would leave the golden candlelight of the dining-room for the starlight outside and sit on the edge of the fountain, cooling our hands in the water and listening drunkenly to its splash and gurgle on the rocks.
'Ought we to be drunk every night?' Sebastian asked one morning.
'Yes, I think so.'
'I think so too.'
The idea that young loves are replaced by higher, more progressive, loves also left its mark.
Waugh was uneasy about this book for the rest of his life, and well he should. He made the young Charles and Sebastian so enchanting that the young reader does not compute that Charles' youth leads him to an unhappy, lonely middle-age and that Sebastian ends up penniless, bald and drunk in some godforsaken African dump.
Hindsight is 20-20, and if I had not been such an ass when I was young--and I vaguely knew I was an ass, incidentally--I would have avoided anything hard-but-classy (like Ancient Greek, for which I simply was not clever enough) and worked my butt off for top grades, so as to go to law school. Alternatively, I could have gotten over my snobby attitude that only "dumb girls" studied French and Italian so as to become language teachers for the district school board. Their pension---aah! What was I thinking?!
I'll tell you what I was thinking--when I was thinking at all, that is, since most of the time I was feeling. I was thinking that I was just going to get a Ph.D. in English Lit on the strength of my delicious writing style, and that bestselling books would just come to me as I gazed from my mullioned office window into an elegant Victorian Gothic quadrangle. A much more important concern was whether I should marry or remain Single, entirely wedded to my Academic Career.
Meanwhile, I spent my five undergraduate years battling a kind of interior fog. It had crept in when I was a teenager, despite loving high school so much more than elementary. What I didn't know then, but certainly know now, is that I suffer from a tendency towards clinical depression.
Sitting about determined to be sad and snarky about everything is a moral failing, but clinical depression is a physical, as well as a psychic, illness. It can sometimes be managed by eating the right things and sometimes by medication. It can be worsened by all kinds of external things. It is a very interesting condition, as I can say at the moment, as I am between bouts. Of course, bouts are hellish.
If you have a terrible feeling that you are just drifting and are willing to do anything, including JUSTGETTINGMARRIED to get it over with, or JUSTSIGNINGTHEPAPER to get it over with, it might be that you have some kind of depression. And if you think you might have some kind of depression, it might be helpful to talk to a doctor or counsellor about it.
I am not a doctor, of course, but I do caution you against using the possibility of being "a depressive" to feed an addiction to DRAMA. I've met too many people hooked on the DRAMA of being on Zoloft, etc. It's not helpful. Really, my vulnerability to depression is just as banal as my youngest sister's vulnerability to bronchitis. The poor child never comes to the UK but she gets the most awful colds. And they go on forever.
Sadly, because I love them, you can't be on my kind of anti-depressants (SSRIs) if you are married and "open to life" because SSRIs scramble baby brains. However, I very much wish I had found out what the fog in my head was when I was 19 and gone straight onto lovely lovely What-Was-It or, actually, I suppose, since What-Was-It wasn't invented yet, its grandmother Prozac. [Update: On the other hand, I see that teenagers and adults under 24 aren't supposed to be on SSRIs, and that they don't work for milder forms of depression, which means most kinds of depression. Oh dear. Well, talk to a medical doctor, if you think you are depressed.]
And now I shall toddle off purposefully to the library to work on my paid article about James III/VIII and Family.