Proteins in cells are among the most complex molecules known. Some proteins react with one another via diffusion or active delivery, but many proteins react via tethers, floppy molecular regions composed of intrinsically disordered amino acid sequences. Tethered reactions are found throughout biology, including the immune system and cell mechanics, and give rise to behavior categorically distinct from non-tethered reactions. We and others have shown that simple models of polymer physics can be used to quantitatively describe tethered reactions. But, even simple polymer physics models are computationally costly to simulate. These simple polymer physics models can be mapped to stochastic processes. This allows stochastic calculus, including rare-event methods and classical tools like the Doob h-transform, to be used to obtain mathematical understanding. We present one example involving the dimerization of formin family proteins, key builders of mechanical structures in cells.