Everyone can agree that people love surprises - that is the reason why we have so many holidays that include gift-giving. It's been a part of our tradition for good reason - it works, and it makes everyone happy. The same goes for relationships - having a partner that is able to surprise you is always a good thing to have, but when the opposite happens, that's when you need to take a deep hard look at things.
If your partner is a source of negative surprises (or is trying in any type of way to spread stress and anxiety to you), that's going to be a negative thing to have. You'll know that your partner is a person that does this a lot, if he also negatively surprises other people in his life, like for example his close friends and family.