If you learn languages you quickly notice that knowing the 99% most frequent words still means that you need to look up a word every paragraph or two and that you have trouble expressing yourself. To write Chinese you need to know several thousand characters, forgetting just a few dozen can be quite annoying when you try to write nontrivial texts.
Being able to write a character by hand, being able to type it up, and being able to read it are all different things. I doubt many Chinese would be thrown off from reading or typing 打喷嚏.
I actually did a deep dive into the issue of unfamiliar characters coming up when reading, and how people handle them. I won't go into all the details, but the general takeaway is:
1. Unfamiliar characters can actually be quite rare or quite common depending on the material you're reading.
2. It's not much of an issue for people either way.
