I don't often run fast, especially when I'm not wearing a bib and timing chip. It's not that I don't like running fast; it's more that I'm a bit afraid of it.
Running fast (or pushing hard in general) puts more stress on the body and the result of that can be injury, in my experience. As a result, I try not to do too much of that unless there's a payoff like a personal best.
I should probably push harder more often than I do though, because it provides training value.
With that in mind, I'm going to resolve to push harder on my shorter runs starting today. A 5km run provides a good opportunity to see where I'm at and compare performance over time.
I ran today's 5km at an average pace of 4:39/km and it was fine. Doing that once or twice a week will build cardio and strength and it'll give me a good indication over time of just how I'm doing.