Simply stated that as a web-developer, this is a critical skill to have. Over the years it's a matter of having the experience to know what you're looking for when trying to find a solution to a problem. That typically comes through sheer will and experience on the job. So although you may not know the answer to every question, you should know how to approach the problem and acquire the solution. Typically in our industry, the internet and several online resources are the go-to for solutions to problems we may encounter. If it's not there, I'll typically collaborate with a team member to gain even more insight.