I sometimes get confused and it looks like they mean the same. E.g.
Success is hard to achieve. Or Success is hard to be achieved.
Can anyone please explain this in detail.
Sometimes the final result of both forms can be the same, but they are different.
This is active voice, which means the subject is doing the action or needs to be doing the action. This means that if we want success we cannot just sit, waiting for success to arrive.
This is passive voice, and passive voice is passive by name and by nature. Here the subject waits for success to arrive, while the hard work behind the success is being done by someone else.
For a general statement, the active voice is better, as it is easier to read/say and has no passive implication. However, if I were devious or a manager, I could force/encourage someone else to do the actual work while I enjoyed the success when it arrived: in this case the passive form would be more descriptive.