The "train" is a vehicle that can transport people or goods on rails. That's the "train". You know modern trains that are quite fast. We have the TGV in France that often uses electricity. At the time, you had steam trains, they were the first trains. Remember that a train is a vehicle that moves on rails and transports people or goods, products. So taking the train, that's what we used to say, is really getting on the train.
"On" is used to say that something is working or is on. If I say "the machine is on" or "the printer is on", it means that it is working. "The washing machine is on" means that the washing machine is working and it is washing, preparing the laundry. So that is something that is on, it is operating, it is working.
The origin of this expression "jump on the train while it's moving" was originally used as a metaphor. A person who arrives in the middle of a conversation and claims to intervene when in fact this person knows nothing about what was discussed before, well we compare that to someone who would have jumped on a train indonesia whatsapp number data when it had already left, when it was moving, it was already on the tracks. So this person who would like to get on the train was not there at the beginning, was not there at the start so this person had not followed everything.
Here, you see the metaphor, eh, it's as good as a person who would jump on a train while it is moving, he would have missed part of the journey, well a person can arrive in a conversation and claim to take part in it when he has ultimately missed a lot.
This metaphor gave rise to the expression "to jump on the bandwagon" which means to arrive in the middle of something, in the middle of an action, in the middle of a situation, without really having witnessed the beginning, having missed the beginning in fact.
As you saw, it can be a conversation, it can also be, I don't know, a football match. We'll take examples so that you understand, but we really use it to show that we arrive in class, in the middle of an action, we missed the beginning.
First example, someone can say: "He arrived late, as usual, so he jumped on the bandwagon, and obviously, he didn't understand anything". So, it can be, for example here, in the case of a meeting, someone arrives late to the meeting and suddenly he doesn't really understand what happened or what is happening because he missed the beginning, he is missing information. Since he arrived late and missed the beginning or missed part of the meeting, he arrives in the middle of the meeting, we say that he jumped on the bandwagon. When we say in the middle here, it doesn't mean that he arrives right in the middle, it means that he missed part of it, he actually arrives in the middle of the meeting.
Imagine, you have two people talking and a third person comes along. The one who comes along says, "Excuse me, what are you talking about? I kind of jumped on the bandwagon, so I'm lost." So this person tries to join a conversation, but since they weren't there from the beginning, well they're a little lost, they don't know exactly what these other people were talking about. To indicate that they've joined in the middle of a conversation, they say, "I jumped on the bandwagon."
Last example, someone can say: "The movie wasn't too complicated, so we were able to understand it easily after jumping on the bandwagon." This example is very interesting. It actually shows you... So here, people say they jumped on the bandwagon for a movie, that means they didn't see the beginning of the movie, they arrived in class. Maybe it was already 5 minutes or 10 minutes or 15 minutes past, but the fact remains that they missed the beginning of the movie and they say: "We jumped on the bandwagon." And luckily for them, the movie was easy, simple, so they still understood the story. But the basic information is that they arrived in class, the movie had already started.