Idealism: behavior or thought based on a conception of things as they should be.
Realism: behavior or thought based on a conception of things as they are.
If whatever your thought can be confirmed by the mind and not with world, then they might have a problem; vise versa. You can start from one, but the other should confirm it.
If Newton's laws of motion was working on papers, but not on reality, then they might have a problem; vise versa. Idealism and realism depends which you are doing--writing a love poem, or building an airplane.
Idealism works great for politicians. But for a realist, it's a brain disease. Realism is the basis of all empiricism, verificationism, science, technology. If realism didn't work, none of those other things would work. And I would point out at this time that I'm writing this post on a realism machine, not an idealism machine.
No matter how hard you imagine running through an open field, if you are indoors, you are going to run into a wall ... because the objective and real wall doesn't give a damn about your subjective and idealistic delusions.