I believe it is flat because that is what I can prove with all of my senses, without outside influence. You believe it is round because you were told it was.
I am not sure this is a useful approach. Do you honestly think it is?
Let me try to explain what I mean.
First, I don't think it has been proven yet that the earth is actually flat. Sure, you may assert that you simply can't see a curvature, but that in and of itself is not proof of it not being a sphere.
Second, science uses cause and effect to 'observe' things indirectly all the time, sometimes very, very indirectly. For instance, no one has observed with their senses the control of electron flow in a transistor or integrated circuit, yet, through several degrees of indirect measurement it was theorized that that is indeed what would happen and through those theories such things like the internet, your computer, TV, cell phones, alarm systems, etc, etc... have been designed and built.
Thirdly, there is imagination. Humans are endowed with very active and useful imaginations. We are not just slugs or ants that solely react to input from their senses. We can and do use our imaginations to do a great many things we cannot perceive with our 5 senses. One of the most useful things it to predict things that have not yet even happened or make assumptions about unseen events. For instance, you may plan a trip around rush hour and you assume traffic will be bad on certain more direct routes due to volume and the likelihood of fender benders, so you plan to use a route that otherwise would be less desirable, but in light of your imagined/predicted/assumed problems on the more direct routes you feel it would be better. In doing so you have made decisions based on something that has not yet even happened, let alone directly observed.
Also, there are things that happen around us all the time that we don't observe but they still affect our lives. Government bodies meet and decide on legislation that becomes law which affects our rights a freedoms. We don't see that happening, but it does. A guy in a foreign country decides to shut down his business and all of a sudden we have a shortage of some doodad or food stuff. A tree falls in the forest and diverts a stream that was used by salmon for spawning and now the salmon fishing is lousy.
Finally, we all rely on things we are 'told' to live our lives. Every day. In modern societies we cannot live entirely by what we can garner from our own senses in real time as we go about our day to day lives. There is just too much to take into account and most of that we can't observe directly. So we follow signs, read or listen to the news and other sources of information, and talk with our network of friends and associates to help us make the decisions we need to make.
So I honestly don't think yours is a truly useful philosophy, and I think it is likely that you don't fully live by it.