I'd guess if you've been doing it for a while it gets to be more a case of 'This is probably going to happen, and then I'm going to solve it this other way.'

If it's all new, it's more of a challenge.

Also - tools. The professionals have the specialised tools, and they know which ones they need. If you're new to the game it's not obvious which tools are required, or even if they exist. (An obvious example being the tap spanner, which turns a horrendous under-the-sink job into something rather easier.)