So again, I'm no rocket surgeon, so please bear with me. Sure, it may not have to be constant effort, but it still takes more effort to get to the moon than it does to get to mars.

So lets consider the following, we have two rockets. Same size, same type, same payload, same engine and same amount of fuel. NASA is going to send rocket #1 to the Moon, and rocket #2 to Mars. They will be launched on days that are the same in literally every way. The mission to Mars will obviously be conducted with Mars and Earth are as close as can be.

So lets say for both rockets it takes 20% of the rocket fuel to get into a decent Earth orbit, with minor deviations to account for avoiding all that fun space-trash us Americans and those Ruskies have been leaving all around (not to mention all the OTHER countries and companies that leave junk in orbit too, but that's a whole other thread).

But for rocket #1 to get to the moon, it takes another 20% of it's fuel to achieve stable orbit, while to leave Earth's orbit entirely, it takes rocket #2 only 5% of it's fuel, then another 5% to accelerate to reach the proper speed so it can go to mars. But that's odd, because it only takes 10% TOTAL to get to and accelerate many many times FASTER to go FARTHER than rocket #1.

Well, again, Rocket #2, once it leaves Earth orbit, doesn't need to accelerate after it matches Mars's approximate velocity. So once it pushes itself out of our gravity well, it's not being acted upon by another planetary body for trillions of miles!

But Rocket #1 is under a pretty much steady (for the purposes of this comment) pull from Earth's gravity. So even though it's going a shorter distance, it must push harder, or push longer. But it's not exactly going down the block. So even though it must use 40% of it's fuel to reach the point where it can obtain a stable orbit, it's still travelling VERY far away. So to us little humans, we only see that it doesn't need to fire it's rocket for 70% of the time, just like rocket #2. But what we didn't see is that Rocket #1 had to push HARDER than rocket #2, as it's constantly being pulled back to Earth. Rocket #1 will make more course corrections much more often than #2, but again, it might not appear to be doing so, as we are only watching it.

TL;DR, Rocket #1 pushes harder, or pushes longer (except for escaping the gravity well, it doesn't really matter if it pushes harder, or pushes longer, as long as more fuel is applied than the minimum necessary to fight gravity), even though Rocket #2 pushes harder.

Remember, the vacuum of space is practically frictionless for all intents and purposes once you're outside a planetary gravity well.