Integrating unit testing into your coding practices can have some positive psychological effects on your programming career.
Unit tests make sure that your new changes into the module will not break existing functionality. This is very common when you have new team member in the project and now he is ready to make changes into the existing module, you cannot expect him/her to be aware of all the past functionality of the module. Now, what if he/she write something which can break existing functionality? Yes, tester will catch the bug but then why waste time to fix the issue when we can catch such issues during development life cycle. This is where unit test will come as a boon.
We should go one step further and integrate unit tests with build process, so we should consider our build successful only when all unit test cases are passed.