Sessa takuma is a Japanese idiom or yojijukugo which roughly translates to mean "to improve together through friendly rivalry by encouraging each other."
Setsu (切) and sa (磋) together mean to cut or scrape something in reference to something hard in order to change its shape and taku (琢) and ma (魔) mean to polish something in order to bring out its natural beauty.
The dojo is supposed to be a place of community where we all work together to improve one another. It is supposed to be a place of sessa takuma.
When we perform the techniques on our partners, we should try and do the techniques to our fullest ability and not hold back. This will enable us to grasp the understanding of how to fully use our power and it will give our partner the opportunity to learn how to fully receive the technique.
However, this doesn't mean that we do it with the intention that we hurt our partners. We do it fully with the intention to make them better. If our technique is too strong, they will have to work harder to take better ukemi. If we hold back our technique, they will never grow or improve. You might be thinking, "What if they get hurt or get mad?" This can happen. If it does, first check your intention and make sure your intention wasn't to hurt them. Secondly, if they do get hurt or upset then you should apologize. Also if you see your partner struggling, you should quietly with hushed tones explain or help them with their ukemi. This is sessa takuma.
We have to remember that our uke is giving up their body for our benefit so that we may improve - which is a compassionate act. Knowing this, we must use this opportunity with the best intention and do our best to not waste their sacrifice. Of course, we cannot abuse them either.
If we can put our emotions and intentions in check then we can push ourselves and our partners to be the best they can be and insure that our dojo is a community which is trying to foster "sessa takuma" or a place where we make each other better.