Properly stored seeds can live for years. Improperly stored seeds don't. What's the difference? Moisture, mostly. It's common to link the amount of water with seed viability, but water activity is a better way to look at the issue.
Prior to germination, seeds need to be stored at water activities that will keep them stable by minimizing enzymatic activity that could reduce their viability but also avoid complete desiccation that will also result in loss of viability. Although the range of viable water activity values is somewhat wide, in moisture terms, a change of as little as 1% can damage germination rates.
Another problem encountered during storage is fungal growth. Knowing the moisture content of your seeds doesn't tell you anything about what can grow in them during storage. Water activity values corresponding with potentially harmful bacteria are well-defined.
Seed priming is most effectively accomplished by monitoring and controlling the water activity of the seeds. Seed priming consists of subjecting seeds to specific water activities to start germination, and then drying them to lower water activities to stop germination. Then, when germination is needed, these seeds are more viable. Attempts to try to do this by tracking moisture content are done, but precise control afforded by water activity increases rates of success.