这篇英语完形填空括号了的mostly能不能替换成obviously

这篇英语完形填空括号了的mostly能不能替换成obviously
答案是mostly,请问怎么判断,这是完型填空选取的原文的片段,完型填空题目有简化.直接搬字典中文意思的勿扰.
When I first started running,it was to lose weight.I dragged myself to the treadmill about once a week,or sometimes just once a month.There was no ‘big goal’,and I was never really that good at it.I got out of breath,my chest hurt,and I made a hundred excuses.It took me a year to run more than three miles.
I wasn’t making much progress,especially weight-wise.( Mostly),it was because I didn’t do it enough.
Then one summer,when the weather was particularly good,I went for a run.Just a gentle jog in the June breeze,and to my surprise,I actually enjoyed it.I ran a couple more times that week,then a few more the week after,and within that month,running turned from a chore to a hobby.
While I was running for superficial reasons (ie.to lose weight) and not making much progress,I would be completely put off by just the number on the scales.I would think,‘What’s the point?‘.But,after that month,I started to truly appreciate running as something fun and healthy to do,not just as a means to an end.
healthier became a part of my daily life,rather than something I begrudgingly tried to fit into it.