I'm a self learner and I find that having a strong sense about my solution is usually good enough. If I feel my answer is brittle then I should simply review the problem statement or anterior definitions and theorem.

I usually look at the solutions when I've come to the conclusion that the problem is just too difficult and typically discover I hadn't thought of something that made the problem accessible. I would argue that if there are sufficient examples within the chapters, not providing solutions to the exercises shouldn't be a problem.

That is unless you have multi-month/research level problems à la Knuth.