As a book editor I once worked with a writer who was a music student training to be a professional musician. I asked her how long she would practice the piano and she said up to seven or eight hours a day. That's what it takes if you want to be really good at piano.
Judo players from sports schools in this country train twice a day. It's not surprising that at national competitions the podium positions tend to be dominated by then. It's hard not to get good if you're training twice a day, five times a week.
Of course those of us who have to hold down full-time jobs or study university courses will find it difficult to train more than a few times a week. But as long as you train regularly (two or three times a week) and train intelligently (that's a topic for another blog posting), you can see significant improvement in your judo.
Then there are those "occasional" judo players who come for training maybe once a month or once every two months. If you've been in judo for any length of time you'll know such people exist. It's one thing if the occasional player is a black belt who has more or less given up on training and just wants to attend a session once in a blue moon. Such a player has presumably already developed his judo to a certain level. It's quite another if the player concerned is a white belt. There is no way the white belt occasional player will see any progress in their judo.
Judo might not require the eight hours of training per day that piano requires but you still need to practice regularly if you want to be good. The thing that I find funny is that quite often these occasional players will shake their heads after training and say things like "I don't know why my techniques are not working". The answer is obvious. They're not working because you hardly come for training!
It's true that some people are naturally more athletic than others. Such people will have a head start and will usually do better than other white belts at first. If that athletically-gifted player doesn't show up much for training though, they will soon see all the other white belts move ahead of them. The person that was so easy to throw is suddenly not so easy to beat anymore. That's when reality bites.
I don't know what it is about judo that makes some people think they can come for training just once a month or less and hope to develop any kind of skills. Think about it. Is there anything in life that you can do just once a month and hope to become good at it? Occasional judo players shouldn't waste their time. If they can't devote the necessary amount of time to train in judo, they shouldn't bother because it will only lead to disappointment.
It's hard enough to become good at judo when you do train regularly. Imagine what it's like when you don't.