First of all, we have the move from the parent's home to the university halls of residence. This requires quite a small vehicle, in fact, you'd probably get away with a small Escort type van that will just hold a couple of bin bags of clothing and some basic supplies that will probably last all of one week.
A few short years later, we have the return move. This is when you realise just how much junk you have accumulated over your first spell at living alone. This is when your removal company needs to be equipped with a slightly larger vehicle. There will be even more clothes than before and, given the way some students live, there will probably be a large amount of rubbish packed, just to be thrown away at the other end.
In a traditional family, and this is by no means the case every time these days, the next move would come when setting up your own home. If you have notice that this event is looming and it's not just a case of your parents becoming sick of you, then you will have time to collect together some furniture in readiness for the life changing event. At this stage, a larger vehicle from the removal company and possibly a couple of large, manly, dark haired men would do the job. Some removal men would also help.
This home, being your first, will be a truly memorable one. It will be the place of so many firsts. You first pay check, your first electricity bill and very probably your first live in partner. This is where you will gather many new belongings and where you will get excited over stupid things like your first very own cheese grater - you would be surprised how we take these things for granted when living with the parents and how much more difficult life is without one!
Next comes moving all this stuff into one household when you get married, or at least get serious enough with someone to consider reproducing. A Luton van is often needed for this trip and possibly, depending on how much of a hoarder you are, there is the possibility of more than one trip being necessary. However, you can relax in the knowledge that it will be quite some time before you need a removal company again.
If you are of the traditional sort and at some time find you and your partner have produced enough rugrats to make this accommodation a bit of a squeeze, then you will be moving on again. This is when you find yourself needing the largest of removal vans. This is when you need those huge vans that you see on the street moving what seems to be a whole tribe from one place to another. For those with a little more sense, the only reason you would need to move to a larger home would be because you have moved up the career ladder and can now afford something a little more spacious - lucky you!
Thus the whole process starts again with the next generation. They, at some point, will be flying the nest with their tiny little removal vans, leaving you and your partner also looking to scale down in the home stakes. Once again, removal vans get smaller as we de-clutter our life and move into smaller and smaller accommodation - anything to deter the grandchildren from staying over - until we end up with minimal belongings in the old folks home.