The back cover of How To Get Control Of Your Time And Your Life, first published in 1973, featured this question, in big red capitals: "What do Gloria Steinem and IBM have in common?" The answer was that both had sought the advice of the author Alan Lakein, "the world's leading expert on personal time management". Nor was Lakein's influence limited to feminism and computing: his system, he boasted, had worked wonders for banks, oil companies, Neil Diamond and the producer of the musical Hair. As if that weren't sufficient endorsement, Lakein also gets a glowing mention in Bill Clinton's autobiography, and there's a man who managed his time in such a way as to - well, to enable him to engage in numerous activities.

There's plenty of wisdom in Lakein's book, which is still in print. But at the core of his system, and many others since, is an approach I'm starting to suspect may be less smart than it looks: prioritisation. List your tasks and label them A, B or C depending on their importance, Lakein advises, then proceed accordingly. (It gets worse: "Label the most important of these A-1 ...") A version of this remains central to how some firms try to encourage staff efficiency; many life coaches, meanwhile, recommend picking one "life area" and prioritising it for a month or year. Yet, though I'm a tragic geek when it comes to tinkering with personal organisation systems, I've never made prioritising work. I used to think the problem was me. Now I'm less sure.

Intuitively, prioritising feels appealing. We're all too busy; we all waste time on urgent-but-unimportant stuff; we like the idea of deciding to address things in order of importance instead. But what does it really mean to make something a B-priority? If it needs doing, it needs doing. "How impressed would you be," wonders my new favourite personal development author, Mark Forster (markforster.net), "if your new car didn't have wing mirrors because the factory thought the engine was more important than the wing mirrors?" And if something's unimportant, why aim to do it at all?

You might respond that some things would just be nice to do if you got the time, but that's a red herring. You won't get the time - you're too busy, remember? - and if something is truly nice, it doesn't deserve relegation to B-status. (Advocates of prioritisation often implicitly link "unimportant" with "fun", as if fun weren't hugely important.) Prioritising life areas is odder still. It makes no sense to rate, say, being a good parent as "more important" than being healthy or financially secure; they're interdependent and, like apples and oranges, not comparable.

Ultimately, prioritisation is an avoidance strategy, fuelled by the illusion that the right system might somehow create more time, and that you might never have to confront the truth - which is that if you've got too much to do, you're going to have to find ways to reduce, not just reorganise, your to-do list. Since I enjoy few things more than reorganising my to-do list, this is rather annoying.

oliver.burkeman@theguardian.com