Trying To Figure Out My New Job

This was my first "full" week at the bike shop. First conclusion: I know jack crap about bikes. It's quite intimidating to have a customer come in and ask you specific questions about a bike part and not know what the heck the person is talking about. It's not just intimidating, it's painful. Hopefully this will change with time. Here's an example - just today I had a customer who wanted a tune up on her bike. Miracle of miracles, I actually replaced a brake cable and made her rear brake work. Unfortunately, I told her that we could replace old, cracked, rotting tires on her bike. I took the old tire off and went to search for a new one, a 26 x 1 3/8 tire. I found some new tires that were stamped 26 x 1 3/8 to 26 x 1 1/4. Close enough, I thought. It ought to work on this rim. I installed the first tire. It did not work. The tire would obviously not stay on the rim. I asked a fellow employee about this and he said, "What you need to do is find a tire that fits only to 26 x 1 3/8. If it has an extra dimension stamped on it, it won't work. And by the way, I sold the last new 26 x 1 3/8 specific tire the other day, so go look in the basement for a used tire that only has 26 x 1 3/8 stamped on it." So I go down to the basement of the shop, and I'm amazed to find two tires of the correct size. Triumphantly, I go up to put these used tires on the rims, and I find the same problem I had with the new tires I had tried previously. I go back to said fellow employee and tell him that the 26 x 1 3/8 specific tires are not fitting correctly and would easily come off the rim. "Oh," he said, "You have 26 x 3/8 Schwinn tires that will only fit on Schwinn rims. If you try them on any other type of rim for 26 x 1 3/8 , they won't work." Sigh. Take that particular situation and multiply it by about 1 million and you'll get an idea of the permutations and combinations of bikes, bike parts and the bike business. The nice thing about bike esoterica is that I'm actually interested in this kind of bike minutiae, as opposed to the specifications of a Hewlitt Packard 8720B with options 001 and 1E1 in my previous job. It will take years of observing and experimenting to feel comfortable in the bike biz, but I want to take that plunge.