1. Jobs are usually much more difficult than they appear to the person who doesn't and has never had that job.
This is a special (and not general) theory because I once had a job--data entry for the Colorado Student Loan center, as a temp worker--that was indeed at least as easy as it looked. Otherwise, my experience has been that all jobs I've had (including other data entry jobs) were harder than they looked.
2. Jobs are usually much more difficult than they appear to the person who used to work the same job but doesn't work that job anymore. The truth of this theory is directly proportional to the amount of time--number of days/weeks/years--that has elapsed since that person had the job.
For example, I used to be a bank teller, but sometimes I get impatient when waiting to make a deposit or otherwise speak with a teller, even though I know it can be a very stressful job. (For what it's worth, I quite my teller job almost 12 years ago, so it's been a while.)