Raise your standards as high as you can live with, avoid wasting your time on routine problems, and always try to work as closely as possible at the boundary of your abilities. Do this because it is the only way of discovering how that boundary should be moved forward.
Dijkstra argues that ability develops most effectively when people work near the edge of what they can presently manage. Routine problems may reinforce existing competence, but they provide fewer opportunities to discover where present limitations lie or how those limitations might be overcome.
His advice also links personal standards with growth. Setting demanding standards creates pressure to improve methods, understanding and judgement rather than simply completing familiar tasks. The boundary of one’s abilities is therefore not treated as fixed: it can be identified and extended through sustained engagement with difficult work.
The quotation does not suggest pursuing difficulty for its own sake. Its emphasis is on challenges that genuinely test and develop capability. In the context of advice to a young scientist, Dijkstra presents this approach as a way to choose worthwhile problems while continuing to increase the level of work one is capable of doing.