Your hamstrings are always tight and you are always stretching them. Or you got a bit smarter and tried to strengthen them with exercises like leg curls, RDLs or bridging.
While all of these exercises can be useful, they are limited either due to high loads, limited position, or poor carry over to close chain movement (aka walking and running) What we need to understand is that to really train a muscle to it's full potential, it must maximally lengthen so it can maximally contract (sort of like pulling back a rubber band more makes it snap back further).
Often, our muscles get stuck in the middle due to sitting, standing and crappy training. Our hamstrings are knee flexors and hip extensors but also influence abduction and adduction.
Here are three exercises I really like that move from maximal stretch to pulling us through gait as they are intended. Give these a go and let me know if you have any questions!