Stress
Honestly, this is one of the best jobs you can have. No, seriously, hyperbole aside, this job is amazing. For one, you get a pretty stellar salary which is fairly hard to come by this day and age. And, because you're probably a very curious person, excited to learn not only how things work, but how to make them work better, you'll enjoy the work it takes to get that hefty paycheck.
Additionally, the more experience you get, the more likely it is that you'll be able to create your own schedule.
That's like the opposite of stress, right?
Well...sort of. That being said, you will work. A lot. As you're starting out, you'll absolutely, definitely, positively be working longer than forty hours a week. You'll have senior engineers breathing down your neck. You'll have bosses, not in the engineering department, mind you, telling you how to do your job, not understanding in the least what it is you do.
So yes, it's a great job, but you'll absolutely, definitely, positively get really stressed out from time to time. Just remember, that fat paycheck can fund a lot of massages and ice cream.