Your niche is the one thing that you could explain to a potential client in your sleep. Your strongest suit - perfected with your experience, background, and education - is your niche. Ask yourself what do you do best and go from there. This should be your first selection. ICP, messaging, and GTM will follow from that point on. IF you fail however to grow your business with your first selection, we will need to get into a quantitative assessment of the reasons for failure, and pivot/find other niches.