Some seed germinate easily; some are hard or tricky to get to germinate because of their dormancy. So why is it that all the species TPP works on are in the 2nd category? Seeds do this for a variety of reasons. If all a plant's seeds germinate readily and something happens to the entire crop, like a late freeze, a generation has been lost. Not so bad for a perennial. However having some seeds that are reluctant to germinate produces a seed bank where not all the seeds produced each season germinate so some remain for the next season. So even if pollination and seed production are terrible, some seedlings may appear from last year's seed. Seeds here in the temperate zone often need a cold period to promote germination, a process called vernalization. Some need alternating cold then warm periods. Some need to have their seed coats etched or softened by a trip through a digestive tract. But then some need to be begged and pleaded with, and still they fail to germinate or germinate a such a low rate as to be useless. What an annoyance! And you often try to imitate natural conditions figuring something out there worked, but there are a lot of variables and it takes considerable time and a lot of fiddling. Part of you wants to solve this problem, this riddle, but so much time has been invested already you just don't want to invest that much more. BTW, seedlings from the field don't like being transplanted either. No wonder so many people work on a stupid little mustard.