Apollonius’s “Conics,” written about 200 B.C., on conic sections, the ellipse, parabola, and hyperbola, is the most complex and difficult single work of all Greek mathematics and was all but unknown in the west until the fifteenth century. This magnificent copy, probably the most elegant of all Greek mathematical manuscripts, was made in 1536 for Pope Paul III. The pages on display show the particularly elaborate figures illustrating Propositions 2-4 of Book III on the equality of areas of triangles and quadrilaterals formed by tangents and diameters of conics, and by tangents and lines parallel to the tangents. In Greek, 1536.
My suggestion is that whenever you have to choose, always choose the unknown, because the known you have already lived. Never miss the unknown. Always choose the unknown and go headlong. Even if you suffer, it is worth it — it always pays.