time of year for seedlings

Is it true that seeds will not germinate at certain times of the year even if you create an environment that is ideal for germination? I have some seeds that are not germinating but are in an ideal environment to grow. I have had had success with seeds germinating in the same environment a few months ago.

Some seeds need stratification, which is essentially being frozen first or spending time exposed to winter conditions before they will germinate. Some seeds don't need this, but just won't germinate until they feel like conditions are right. For example, lettuce seeds don't really need to freeze to germinate, and I have volunteer lettuces show up in spots I grew lettuce in 2 years ago. I also have lettuce and dill for that matter emerging now that I sowed new back in the spring of this year. Sometimes seeds can be finicky for no rhyme or reason it seems (to me at least).