You take pride in your ability to do your job well. You work hard to gain experience and knowledge that you can use to solve problems.
Yet every now and then you get stuck. You try to solve the problem using the same processes you always do, processes that always work - except that this time they don't. You still have a problem you can't solve, and you can't figure out why.
So you try everything you know, think of everything you can, all to no avail. Your inclination is to dig in and work harder but the likely result is that you will still just repeat things you have already tried, and which did not work.
Accept the fact that it is time to ask for help and recognize that in this case all your knowledge and experience are just not enough.
Ask a subordinate to help you. You can explain the problem-solving process that has always worked and let them do it. It is possible that you have done it so many times that you are unknowingly taking shortcuts and skipping a crucial step.
Call over a colleague and have them listen to you as you explain the process. Allow them to interrupt you, and ask questions when they do not understand something. The questions they ask or the answer you give may jog something in your brain that gives you the answer you seek.
If no one is available to help you, brainstorm with yourself using a very simple technique. On a sheet of paper, list each step of the process, then ask "Why do I do that?" or "Why do I do it that way?" This will give you the insight you need.
So remember when you get stuck you know a lot but you don't know it all - and you never will. Don't let your pride keep you from getting help and solving the problem.