爱华网分析下吧，这句的翻译大体涉及这么几个要点：‘大道至简’的哲学思想、其在上下文中的意义取舍以及‘任性’的表达：
大道至简的含义（1）“就是最有价值的道理其实是最朴素的道理，很重要的道理其实是很平常的道理。大道至简应是一种境界，也是一种哲学...”（2）“大道理（指基本原理、方法和规律）是极其简单的，简单到一两句话就能说明白。”（3）“大道从最简单处入手。老子说，为大于细。从简易处入手，并不是说大道本身是简单的。”
要做好翻译首先得理解原文，来看下该句的出处（context）：政府工作报告（讨论稿）第三部分“把改革开放扎实推向纵深”中的一段：“地方政府对应当放给市场和社会的权力，要彻底放、不截留，上级下放的审批事项，要接得住、管得好。加强事中事后监管，健全为企业和社会服务一张网，推进社会信用体系建设，建立全国统一的社会信用代码制度和信用信息共享交换平台，依法保护企业和个人信息安全。大道至简，有权不可任性。各级政府都要建立简政放权、转变职能的有力推进机制，给企业松绑，为创业提供便利，营造公平竞争环境。所有行政审批事项都要简化程序，明确时限，用政府权力的“减法”，换取市场活力的“乘法”。”
根据这个出处基本可以确定“大道至简”的意义在此应该是上述（3）的意思。
‘任性’的表达：
“任性”一词在英文里可以找到这些：
capricious(changing quickly andsuddenly变化无常的任性),
headstrong(very determined to do what you want,even after others advise not to do it: an impulsive headstrongchild固执的任性),
self-willed(very determined to do what you want,even when this is unreasonable: a wild and self-willedchild不理智的任性),
intractable(having a strong will and difficultto control: They found the ilanders intractable, resistingtheir offers of gifts),
unrestrained(not controlled or limited:unrestrained laughter无拘束无限制的),
wilful (continuing to do what you want, even after youare told to stop顽固的任性),
wayward(behaving in a way that is differentfrom other people and that causes problem: a waywardteenager恣意妄 为的任性),
unruly (behaving in a uncontrolled way: unrulychildren蛮 横的任性)
rash(doing something too quickly, withoutthinking carefully about whether it is sensible or not: don'tgo making any rash decisions about your future!轻率的)
这些词哪个能完全表达我们目前网络热词儿“任性”的含义呢？在李总理之前的答记者问上翻译随机用了capricious其实也不贴切，这个词说的主要是情绪反复无常的那种任性。而分析总理所使用的‘任性’本意应该还是不能‘乱来“之意，所以还是’abuse‘一词达意。
句子逻辑及译文
如上所述，这句如使用power做主语，逻辑上应该是：
Complex doctrine dwells in simpleprinciples, powers should not be exercised at will. 或
Complex doctrine dwells in simple principles,powers should not be abused.
如使用人做主语：Complex doctrinedwells in simple principles, No oneshould abuseits powers.
但是本句并非独立存在，其需服务于上下文。因此考虑到英文段的逻辑以及“简化”一词在政府文件及答问翻译中所使用的‘streamline’，这句译成这样更合适些：
Complexdoctrines should bestreamlined, and powers should not be exercised atwill.或
Complex doctrine should be streamlined, andpowers should not be abused.
感谢“法律英语”所有群友，下面是勤奋的群友贡献的智慧(3月6日）：
@Tiffany Shen: it goes withoutsaying that powers should not be abused.
@Laura Liu: The rule is simple. NoPower should be abused.
@俊哥: As a truth without doubt,powers may not be executed at will by its holders.
@王法师: It's a simple truth thatpowers should not be abused.
@唐晓丽: To put it simply, those withpower shall not be capricious. 这里的任性其实可以直接用capricious.
@万千会: It goes simply that powershouldn't be held headstrongly.
@Danielzhuang: In summary, thepowers should not be abused.
@展豪happy：The greatest is thesimpleast. Power should never be irrationally exercised.
@锟先：Good governance is simple,accountability shall always be together with power or you shall notabuse your power .....shall not use your power at will.
@邢超 @远 中文
Some source/reference:
