I know I'm prejudiced, but I don't think it helps to be a huge success early in life. Too much struggling to keep up the good work, too many people saying (cf, Woody Allen) that they liked the earlier funnier stuff better, too much of a sense that life is a long, slow dwindling of glory. Look at John Irving (still most famous for The World According to Garp) or Martin Amis (Money) or Jay McInerney (Bright Lights Big City).  What you really want in a career is a nice slow burn, a steady development so that (like, say, Hilary Mantel) you write your great novel late-ish, when your mind is clear, you don't believe your own press, and you're less likely to blow the profits on cocaine and stupid clothes.

Of course you can get it wrong in the other direction, like Van Gogh, and (despite wondrous talent) only achieve recognition after you're dead. This also shows poor planning.

When my husband worked in Nepal, he says he remembers watching, bemused, as huge, musclebound climbers powered past him at great speed through the astonishingly beautiful Himalayan foothills, looking neither left nor right, eyes locked on the summit of Everest.

The journey is the destination. Worth remembering.