What semantic field underlies 涵 for it to mean 'soak, immerse' and 'tolerate, be lenient'? Fortunately I can guess a possible ratiocination of this etymology: 5 Houseplants You Can’t Kill by Overwatering. Because these plants won't die even if soaked, immersed, or wet, they can tolerate, forigve your over-watering. They are lenient to the wrongdoing of over-watering. Am I correct? I screenshot Yellowbridge. 


涵 - Wiktionary


  涵
  
  
  to soak; to wet
  to tolerate; to forgive; to be lenient
  to immerse
  a culvert
  Alternative form of 含 (“to contain, to bear”).
The semantic extension is as follows:


To be soaked in water
To have a large capacity to hold water
To have a large capacity to tolerate bullshit
To be lenient (e.g. lenient on someone for their wrongdoings)




References:


《漢語大詞典》