Seriously it's like going to golden corral and being told to pick one thing to eat and nothing else.
Could I get by with only one? Probably. Is their one knife to rule them all? Certainly not. The most well rounded knife I own is my customized Manix 2. But it's uncomfortably heavy while wearing hybrid or linen shorts. So I look to my Twist Tighe OTF, Civivi McKenna, or other smaller lightweight knife. On average, they can handle most things I might run into at a desk job. I keep a Vic Super Tinker in my bag always.
When I go to my sister's house, it's my Heretic Manticore E. Medium weight and size, pretty robust blade, and with four little ones around, it's too hard for them to open, and if dropped it won't accidentally open.
If I'm helping someone move, or something similar, I carry my Gayle Bradley. Its well used, tough, can handle just about anything. And if I let someone use it for a moment, I'm not too worried it will break.
I think it's stupid to limit oneself in such away.
I'm a special case, but fidget factor is big to me. I have severe anxiety and flicking/flipping open and closed helps me calm down instead of medicine. Yes I'm constantly adjusting the pivot on my knives because they off center, but it's great relief.