'No, we aren't the same,' Eldrian thought, 'but it is undeniable that us gaining power from killing means we steal part of our enemy's XP... I wonder, is there perhaps an amount one can lose without issue?' Eldrian felt this must be the case; else, using lifeforce in any way should always lead to significant damage to oneself.
There must be some threshold of lifeforce that isn't needed to sustain one's 'self'. 'I wonder, do the AI ensure that what we take is only this 'safe' portion of XP? Perhaps what can move on to the realm of souls is limited even? Thus a portion always dissipates, and this is what other living creatures absorb upon killing one another? Or perhaps absorb simply by being near them, or eating their flesh in the case of animals?'
This felt like an excellent theory to Eldrian. He knew that almost everything had levels. Plants were perhaps the only exclusion, but it might simply be that he couldn't perceive their levels.