It was so nice an afternoon that I decided to go for a walk in my new boots---the ones I'd seen advertised on TV as ''the world's best boots" Well,in theory,yes,they were very comfortable boots but I soon found that in fact they gave me blisters.
那实在是一个很美好的下午,我决定了穿上我的新靴子去散一次步——就是在电视广告里看见说是"世界上最好的靴子"那一那双了.不错,在理论上,它们是一双非常舒适的靴子,可是,很快地我便发觉其实它们竟然使到我的双脚起了水疱.
楼上朋友没有错,in theory 就是〔理论上〕的意思.