Most people who have boxes are scared of opening them. One of the most powerful things I did in NLP had me shaking and crying before doing it - and that was only while we were discussing the process! But of course, as part of the training, we were supposed to then practise the exercise and that was what had me going. But my teacher saw me, ended the class a little early, sent everyone else off and basically cornered me and made me do it.
I had some kind of barrier well in place against the feelings that were coming up - but he was a very skilled NLP therapist as well as teacher and he managed to get me past the barrier where I found the "feeling" that I'd suppressed for so long. And then the exercise took me through that and out the other side to the most fantastic place. Well worth it, one of the most amazing experiences of my life and very liberating. It also made me damn certain that I would never inflict that feeling on my DS (not that I had him then, but I remember it so well, when he came along I made sure he wouldn't get the same).
I had one client who had been put through terrible times with her mother. She had dreadful issues herself because of it, but the box lid kept fighting to be removed - and every time it did, she would sink into the most dreadful depression, rage at everyone and everything, to the point where she had to be admitted to a psych unit for everyone's safety. But she could not, would not, dare not ever let the lid off the box - every time it came loose, she clamped it down hard - and it made her so unwell.
If you like to think of it another way, it's like a festering pus-filled wound. You can keep covering it up, hoping that it will go away, but until it's exposed to the air, cleaned and allowed to heal, it's going to go on chewing away at your flesh, even if you can't see it - and it's going to hurt you all the more while it's not healing. Could even go gangrenous, or give you septicaemia - physical wounds need to be healed so they don't inflict more damage, and the same goes for mental wounds.