Budgets usually have tighter limits than wish lists. What strategies can be used to avoid wasting money on equipment?
By "wasting", I mean spending on an expensive item of photography equipment to solve a problem and then finding it frequently fail at solving well the problem it was supposed to tackle. The inability should be attributable to the product's design, not breakage of a specific item or inexperience with such gear.
I felt a recently closed question about useless accessories had some potential for taming the widely spread constant need for new equipment and bringing out some marketing hype, so I'll try to ask a similar question in a more constructive way.