Concentrating the mind on a fixed object allows one to overcome obstacles. Usually, the mind is fixed on a single tattwa (principle of truth).
It is highly important to fix the mind on the same tattwa. Use the same mantra, symbol or aspect of the breath. If one keeps changing, the mind will become confused and it will be difficult to achieve sustained efforts of concentration. If we keep the same tattwa, eventually the mind will become sharp and one-pointed.