            By 1912, however, Einstein had reached an impasse  , realizing that he needed to go beyond the mathematics that he knew and was familiar with.
<meaning-changed>             By 1912, however, Einstein had reached an impasse  , realizing that he needed to go beyond the mathematics that he knew and was familiar with.
 By 1912, however, Einstein had reached an impasse in his kinematic development of general relativity , realizing that he needed to go beyond the mathematics that he knew and was familiar with.