Boundaries are vital to your self-esteem and self-confidence, because when you speak your truth, you are honouring yourself which builds your self-worth.
It's easy to forget how important boundaries are for your emotional wellbeing. If you suffer from low self-esteem it can be even harder to hold them, particularly with others who may use guilt, emotional blackmail, dismissive or dominating behaviours to push at your boundaries.
Remember that boundaries are not barriers. Having them does not make you cold or uncaring and it doesn't place a barrier between you and others. In fact, its usually the opposite! People often respond surprisingly well to boundaries because you are telling them where they stand and this helps people to feel safe.
If you are someone who has not held boundaries in the past, others might seem surprised or shocked when you draw a line. Don't let this worry you, it is up to them to adapt and people often do. If someone doesn't wish to adapt or honour your boundary, that is their choice and not your responsibility. It also raises an interesting question - has this person benefitted from you not having boundaries in the past? If so, this might explain their reluctance to honour the line you have drawn.
There will be people who try to push you boundaries. Be kind but firm with your boundary, you don't have to explain yourself, in fact its better to avoid over-explaining. Simply repeat your stance and excuse yourself from the conversation if you have to. How someone reacts to your boundary is their responsibility, not yours. You own your boundary and they own their reaction.
Boundaries are one of the building blocks of self-esteem. When you honour yourself by saying no, standing firm or drawing a line, you are honouring your sense of discomfort with something or someone. Honouring your feelings is vital in building self-esteem.
If you get used to holding boundaries, your self-esteem will grow because your feelings matter, they are part of your inner truth. You inner truth is the place from which everything grows from there anything is possible.