First let me say your question is very open to interpretation. Their are a lot of things that are not fun. Waking up at O-dark-thirty to run in the rain or snow only to get back well before breakfast to shower as the starting part of your day isn't fun but it also isn't hard. Fact, of the matter some people really miss it after getting out. The food is generally good. Yes, its true! Working long days is hard to get used to but if it is the first real job you have ever had you will get used to early wake-ups and late hours to finish the mission. There is a lot of down time and some people don't know how or can't learn on how to fill the down time up productively but its not hard, you just do it. The truth of the matter is that you can stay very busy for 20 years and learn alot with a lot of people without doing anything really hard.
Unless of course you want to be the best. The Best in every field work harder than the rest. They fill up the down time by educating themselves when no one else is. They end there work day with more physical training and don't go out drinking all night. They become a technical expert where people start to notice that they are the best and ask for there help. They are asked to attend more schools, get pushed to more responsible positions, and grow as a person.
You see the military is a great place to be, because if you don't mind a little discomfort, you can push yourself to do the hard things in life and become something you never knew you could be.