This is critical. Without looking, solve it again. If you succeed, you truly learned.
However, while these reasons are sympathetic, they do not justify piracy.
Microelectronics is a hierarchical subject. If you do not understand the small-signal model of a MOSFET in Chapter 5, you will be utterly lost in Chapter 6 regarding differential amplifiers. A solution manual acts as a scaffold. When a student is stuck on a specific bias point calculation for hours, seeing the correct setup can unblock the learning process, allowing them to move forward rather than abandoning the problem in frustration.