"It seemed like a good idea at the time &"
Yes, those are the famous last words of many NBA general managers. That's because investing a considerable amount of money in any player, whether he has a track record of production or seems certain to deliver on clear promise, is always is a risk. And the reasons a GM goes big on a deal are many. Maybe the player perfectly fits your team and the system your coach runs. Maybe someone on your staff vouched for him. Maybe you feel you're just one player away. Maybe you're not a destination city and you feel you have to pay a premium to add talent.
So the GM massages the numbers and makes it work; a lower starting salary with maximum raises shifts the weight of the contract toward its end. The thinking is the player will eventually be worth the deal, or at the very least, he'll raise his value so you'll be able to move him far before those higher salary years arrive.
The problem is the plan is set around a best-case scenario. It doesn't adequately protect the team from unforeseen complications, of which there can be many.
Now you're stuck with a "toxic" deal: the type of contract you can never trade away without including heavy sweeteners (draft picks or promising young talent) or receiving an equally or more toxic deal in return. In the new CBA, financial planning is as important (if not more) as talent evaluation, as teams cannot afford to squander limited resources for marginal productivity.
Here are the most toxic deals in the NBA. These are the contracts that nobody wants to deal for without receiving heavy incentives.