Up voted, although I think 'wasted' is a bit harsh. I would call lost time to unsuccessful research a necessary cost. If we all knew exactly which problems to study and which approaches to use it wouldn't be research, it would be divination.
I read the quote not as saying that four-fifths of his time had no value at all but that so-called 'wasted' time is a necessary part of the research process and actually does have value.
Every month on the month, Less Wrong has a thread where we post Deep Wisdom from the Masters. I saw that nobody did this yet for December for some reason, so I figured I could do it myself.
* Please post all quotes separately, so that they can be voted up/down separately. (If they are strongly related, reply to your own comments. If strongly ordered, then go ahead and post them together.)
* "Do not quote yourself." --Tiiba
* Do not quote comments/posts on LW/OB. That's like shooting fish in a barrel. :)
* No more than 5 quotes per person per monthly thread, please.