A problem in the Schubert Calculus
    In space, there are 2 lines meeting four given lines (Here in blue, green, red, and black).

    Indeed, the blue, green, and red lines are members of one ruling of a unique hyperboloid of one sheet. Members of the other ruling are the lines meeting these three.
    The fourth black line meets the hyperboloid in two points, and through each of these points is a line meeting our four given lines.
    If the black line misses the hyperboloid, then the two solutions are complex conjugate.
   

The Shapiro Conjecture (Theorem of Mukhin, Tarasov, and Varchenko) is a way to choose the 4 lines to ensure that both solutions will be real.