Let's do simple math! More destruction means you will struggle to succeed. Now let me relate this statement with some reasons why we need to set boundaries.
You care too much about 'what others will think' and 'how your self-image would be' and that's why can't set boundaries; which means you got more distraction and things to do for others than your own and as a result, you lag behind from your personal goal.
Setting boundaries in our relationships, in our way of life, is nothing difficult. But as I was saying, we either don't have the right intention or we fear/care about something that doesn't matter much in our life. But there are many ways that can help us set some boundaries so that we can be focused and less distracted.
Be clear about your desire and reflect them through your work. Be in such a way so people would not demand what you can't do. Don't live for others. Be clear to yourself what your really want, your purpose, and show it.
Have rules in life. Set some simple to hard rules like how much you will drink or how much tolerance you would show to your relationship.
Learn to say no. Not only that know how you can exit from a situation you don't want to be in. Believe me, this practice will save your time, money, and will help you keep focused on your own life.
Let others know. Personal boundaries can't work alone, you have to show your boundaries so people would understand you more. Also, it helps to remind ourselves of what we can and can not do.
Start with setting some very simple rules and boundaries in life. Notice how it shapes your life and makes you more disciplined. You will gradually understand why it's necessary to set some boundaries to increase success!