Consider $P^{2}(\mathbb{C})$, the space of all lines through the origin in $\mathbb{C}^{3}$ (or $\mathbb{R}^3$ if that works better). Let $X\subset P^{2}(\mathbb{C})$ be a (nonempty) hypersurface (algebraic in some coordinates). Must it be the case that for some $2$-dimensional subspace $V$ of $\mathbb{C}^3$, $P^1(V)\subset X$?
More generally, given $1<m<n$, must $n-1$-dimensional hypersurfaces in $P^{n}(\mathbb{C})$ (for $n\geq 2$) contain a $P^{m-1}(V)$ for some $m$-dimensional subspace $V\subset \mathbb{C}^{n+1}$?
I'm not a geometer (set theorist in unfamiliar waters here), so I don't have much of a feeling for these questions or the techniques involved, but my understanding is that one can show (using cohomology or Schubert calculus) that every hypersurface intersects every projective line.