As others have said, that's basically the case. Most of the complexity, though, is at the bottom, in the engines. Absolutely incredible machines designed to withstand—and control—incredible forces. Turbopumps spinning at tens of thousands of revolutions per second. Insane amounts of heat that need to be cooled so the engine bell doesn't melt. Handling cryogenic fuels (liquid oxygen is very, very cold!) at very high pressures, moving them at very high speeds.

One failure mode, out of the many many possible failure modes, that's particularly interesting to me is that if the pressure in the pipes going into the turbopumps (which push the fuel into the combustion chamber fast enough to keep the explosion going) is too low, then you'll get cavitation on the back of the turbopump blades, and the forces from that will destroy the turbopump in under a second. Kaboom.

Oh, also, these pumps have to spin so fast that they themselves are driven by essentially little mini rocket engines.

For a visual depiction of the complexity of rocket engines, check out SpaceX's Raptor engine, arguably the most advanced engine being produced right now: https://imgix.bustle.com/uploads/image/2020/4/6/c1349369-162...

I'm no rocket scientist, though, just an interested amateur. Real rocket scientists please correct me if I got anything wrong!

Fundamentally the purpose of a rocket is to throw mass behind it very quickly. The idea is pretty simple but the implementation turns out to be quite complex.

Almost all the engineering magic and weight is at the bottom: nozzles to handle very high temperatures, high-pressure high-speed turbopumps, and so on. The falling Falcon stages have the aerodynamic stabilisation of a shuttlecock, and their low center of gravity helps them be stable on fairly small legs.

As someone who knows quite a bit about rockets, they really are for the most part this primitive. Just these tubes filled with fuel, with a few volts of angry pixies at the top controlling a few degrees of gimbaling at the bottom.

That's pretty much what rockets are: massive fuel tanks and a ton of hardware to keep the resulting explosion under control.

The really hard part is keeping the explosion intentional and pointed where you want it to go.

Yes, we'll have to find a new phrase for "rocket science" :)