Something I still remember from my school days was one of my teachers telling me, "David, don't be afraid to ask a question!". Presumably I'd been struggling with a particular topic (possibly maths), and essentially they were encouraging me not to sit there "spinning my wheels", but get some help to make sense of the problem.
That's a lesson that's just as applicable today as it was then. In software development, we are constantly solving problems. Some are easy, and some are hard. Some are easy but the hard bit is finding the bit that will be easy to fix.
Sometimes it's just the act of getting a colleague to come and have a look that sheds light on the problem.
But not just in work. Only this week I was at a Church meeting, and people were asking some very deep, insightful questions. I however asked what some might call a "dumb" question (but one which I didn't know the answer, hence why I asked).
After the meeting as I was leaving, a couple of people came up to me and said, "I was wondering the same thing, thanks for asking that!".
Which is another great reason to ask questions, even if you think they're dumb, as odds are someone else is wondering the same thing too.
Photo from Mallala Museum, used under Creative Commons Attribution-NonCommercial 2.0 Generic license