Sometimes it’s hard but to be honest I would rather have a job that was sometimes hard because it means I have to use my brain which is fun. Jobs that aren’t hard can often be boring and I woudn’t enjoy that.
I agree with Ed, sometimes it can be very hard, or very tough to do. For example when my lasers are not working properly I can spend maybe 2 weeks trying to fix it, which starts to wear you down after a while. But if it was always easy and straightforward I wouldn’t find it close to as fun as I do now.