"I want to be able to touch my toes without pain."
This is easily one of the top requests people new to yoga have. It seems so simple: your toes are right there so why can't you reach them? Hamstrings are the bane of many students' yoga practice. Students may feel frustrated that they've come a long way in other aspects of their practice, but then those hamstrings speak up a little too loud and put a halt from touching those toes.
Within a few months of starting my yoga journey, I signed up for a 30 day hot yoga challenge which was to do a 90 minute hot yoga practice every day for 30 days straight. Little by little, my body became more malleable, but I felt like my hamstrings weren't progressing the way I wanted. In the third week of the challenge, my ego spoke up and said, "Who do those hamstrings think they are? Let's show them!" While in a wide legged forward bend, I decided to muscle my way further in hopes of getting my head closer to the mat. YELP! I pulled my hamstrings in my left leg and nearly collapsed (my head could have touched the mat after all!). The rest of my practice was painful, I couldn't do many poses, and I limped my way out of the studio. The homestretch of my 30 day challenge was hindered because of my ego. I did finish the challenge, but it clearly wasn't the glorious outcome I had envisioned.
On a genetic level, some bodies have short hamstrings and no matter how patient a student is or how much they practice, their body is simply designed that way. Every body is different.
Genetics aside, many students new to yoga have tight lower backs, tight hips, tight quads, and thus stubborn hamstrings. Forcing them into a pose is only going to get them to tense up more and be more susceptible to injury. It seems like an easy enough goal to touch your toes, but yoga is not a competition or a race. Relax, breathe, and be patient with your hamstrings and with yourself. You may find that being patient with your body will help you to be patient in other situations in life; that it's not always in your best interest to force an outcome.