opportunity cost

Here is the link to the Wikipedia article on this topic.
The Wikipedia article makes no distinction between levels of activity, for example, idle amusement versus study, nor does it bring in the effect of inertia to the discussion. Choosing idle amusement over study not only means loss of that amount of intellectual development, but also brings an increase in the propensity to make a similar choice in the future. (Hence the advice, “Don’t have any fun until you’re fifty.”, and the advice, “Lead simple lives, so that you may do complicated mathematics.”)
[continuous improvement]