"I didn't try hard BUT succeeded"
--> since you are using a positive and negative situations within the same sentence, you should be using "but" to connect them.
"I didn't try hard SO didn't succeed"
--> since you are describing an outcome from an action, you should be using "so" to connect them.
- "and" is only used to connect similar items or make indicate the end of a list.
- "didn't" can usually only be used a maximum of twice within the same sentence to reference two different points within it; however, if you are making of list of things that you didn't do for example, it is best to just use it once and then list the thing after using a comma to separate them.