It means that you have tried your best. Whether you can achieve your goal depends on your luck. The idiom "It is up to people to plan things, and it is up to Heaven to make things happen" tells everyone that when doing things, we must learn to treat and correctly handle the relationship between people and things, process and results. It must be understood that everything comes from a good place. Only by working hard can things come naturally.
It is up to people to plan things, and it is up to God to make things happen. Both are indispensable. To achieve a certain goal, planning is the first step that must be completed. Only by working hard and constantly "seeking" can we lay a good and solid foundation and necessary conditions for the realization of results.
Extended information
In ancient times, science, technology and information were underdeveloped, and the means that people could use to make major decisions were very limited. Divination, astrology, night observation, etc. were all commonly used Means, and these things are basically unreliable, the decisions made are not very reliable. On the other hand, at that time, the equipment was crude and the ability to resist risks was extremely weak. Marching and fighting were greatly affected by natural factors such as weather, sometimes even decisively.
Therefore, decisions made based on a limited amount of information still face many uncertain factors during execution, and no matter how careful a plan is, there are variables. After making a decision, people often say, "It's up to people to make things happen, and it's up to God to make things happen." This actually means that you don't know what to do, and you are adding insurance for possible failure.
If you are successful in the implementation of your decision, in order to show humility and prepare for possible failures in the future, you can say "Man plans, success depends on God" and give credit to God. This is actually a sentence. It's just modest words that don't mean anything. If you fail, just say, "It's up to people to plan things, but it's up to God to make things happen."