People often find themselves confused about whether the person they're attracted to, talking to, or dating reciprocates their feelings. This uncertainty often stems from what seem to be mixed signals, particularly when the other person alternates between showing interest and disinterest.
Consider your behavior when you're genuinely into someone. You typically respond quickly to their messages, eagerly start conversations whenever possible, and make an effort to meet up whenever you're free. In this scenario your intentions are clear and straightforward.
Now, contrast this with how you behave when you like someone but aren't as strongly attracted to them; they're just "alright." Your motivation isn't as strong in this case. On good days, you may feel like chatting and making plans, but other times you might read their messages and forget to respond, preoccupied with other things. Perhaps you've even arranged meetings but canceled, coming up with some excuse not to. You wouldn't do these things with the one you really like.
Basically, so-called mixed signals are really just a sign of lack of interest - it's as simple as that.