We should start using the mind as a tool, he argues, instead of letting the mind use us, which is the normal state of affairs. When Descartes said 'I… - Oliver Burkeman

In order to most fully inhabit the only life you ever get, you have to refrain from using every spare hour for personal growth.

Perhaps you don't need telling that self-help books, the modern-day apotheosis of the quest for happiness, are among the things that fail to make us happy. But, for the record, research strongly suggests that they rarely much help. This is why, among themselves, some self-help publishers refer to the 'eighteen-month rule', which states that the person most likely to purchase any given self-help book is someone who, within the previous eighteen months, purchased a self-help book – one that evidently didn't solve all their problems.

The truth, then is that spending at least some of your leisure time "wastefully", focused solely on the pleasure of the experience, is the only way not to waste it - to be truly at leisure rather than covertly engaged in future-focused self-improvement.