The challenge of the second Beatitude is to grieve, to mourn, to be heart-broken over your sinful condition and each time you sin.
I believe Jesus is calling for a zero tolerance policy against sin in your life.
Obviously, that is not to suppose you will never sin, but it is to say you should never willfully sin AND the moment you do sin grief should flood your heart.
If you hope to be free from sin, you must guard your mind! Diligently stand guard over your mind and take every thought captive.
Be intentionally careful HOW you think and WHAT you think about! If there is something you shouldn't think about, don't give it a second thought! In fact, don't give it a first thought!
Only allow your mind to entertain thoughts of things that are true. If it isn't true don't give it entry into your thoughts.
Only permit things that are honorable to enter your mind. If it isn't honorable don't inflict your mind with it.
If it is not something that is just, don't give it a thought!
When something is not pure, it is not worthy of a thought!
Only meditate on things that are lovely, commendable, excellent or praiseworthy, fill your mind with those things!
You cannot have a corrupt or impure mind and have a pure heart.
Stand guard at your heart and mind! Do not allow any sin-inducing thought to dwell in your mind. Instead, nurture your mind with the true Word of God.
The best friend of a happy heart is a healthy mind!