Just in Time (JIT) was popularized by Toyota for its car manufacturing. The purpose is to avoid the seven wastes: overproduction, waiting, transportation, inappropriate processing, excessive inventory, unnecessary motion, and defects. This system is also known as lean production.
Just in Time for Side Projects
Because of very tight time constraints, we have no choice but carefully picking the tasks from our todo list. Just in Time is another tool for choosing the right things.
When building an app, reading competitor's long feature list page often overwhelms and demotivates us. But what really needed to be available in the first version are only the core features and the one that differenciate.
When Kiamboy released for the first time, it didn't have chart feature for showing the statistics of user activities. The chart feature was added in the following release. Statistics only make sense when a reasonable amount of data available. So why implementing it from the beginning. You can wait for some time until there are users that have enough data to process.
Another common example of later-to-be-implemented feature is payment. Many services just put "coming soon" on their payment page. Just wait until many users start using the app.
There are many features that we don't need in the beginning especially when we are still not sure if the product will get traction or not. Just focus on features that needed to validate the initial hypothesis.
Just in Time Learning
If you are a developer, you might often experience this. Before implementing something, we often think that we need to learn first. We read and watch every tutorial we can find. We spend a lot of time from one tutorial/video to another. We fill our days consuming whatever material that seems related to the things in our todo list.
That is a waste of time and you don't really learn much by reading or watching a tutorial anyway. The best way of learning anything is by doing. So, what I did recently, I stop reading tutorials in advance. I just wait until I start implementing the feature and then try to find the tutorial only when I get stuck.