1. The soil was too wet
   <Sung solemnly to a Simon and Garfunkle tune>
     Hello, mold, my old friend. I've come to talk to you again! 
2. The soil wasn’t wet enough
   "Someone" forgot to moisten the soil before planting.
   (It was me. I forgot to moisten the soil enough before planting.)
3. There wasn’t enough light!
   The grow light timer wasn’t cooperating.
4. There was too much light!
   Forgot that those seeds needed darkness to germinate...
5. I forgot to plant the seeds...
   Hands up for anyone who has prepped a tray for seeds and managed to overlook it!