In this photo, the triangle (bottom left) has been sewn to another triangle using a ¼ inch seam allowance. It is a good idea to use a ruler to check your seam allowance when you first begin quilting as it is most important to be accurate. If you do not sew an accurate ¼” seam, your patchwork will not match at intersections.
In this Tree of Life block there are many seams. If you were off just a 1/16” when sewing each pair of triangles, this would cause you to come up short ¼” or more in each row.