If I expect something to happen (or not happen), then if my expectation is not met, I will automatically think something is wrong with me, and/or something is wrong with another or others, and/or something is wrong with God/the universe. Expectation is blame waiting to happen. Expectation is setting yourself up to be a possible victim. “I expected that we would never get divorced. But, after what that bastard did, I couldn’t live with him any longer!”
Expectation is distinct from intention, prediction, or commitment. You could create any one of these three without also creating an expectation. If you created an intention, prediction, or commitment without, at the same time, attaching an expectation, then the lack of fulfillment of any of those would not occasion an upset.
The benefits that habituate us to creating expectations are two short-term benefits that we can cash in on. The first short-term benefit is that it allows us to feel more confident (thereby reducing fear and/or sense of risk) that whatever we expect to happen (or expect not to happen) will actually occur the way we expect. The second benefit is that it allows us to count our chickens before they hatch, getting to create enjoyable excitement and anticipation that we might not be able to feel if we fully acknowledged the risk that our projected results may not come to pass.