“The concept of proportionality is at the very core of the modern understanding of human rights. Proportionality is, first and foremost, a condition for the limitation of a qualified fundamental right. In other words, regardless of the scope of a constitutional or quasi-constitutional (ie primary European Union (EU) law, and the Council of Europe’s European Convention of Human Rights (ECHR)) right, proportionality constitutes the main criterion through which the extent of such right’s protection and realization are assessed. Proportionality, as a general principle of EU primary law, is also used to distinguish between the competences of the EU from the Member States’ ones. Beyond the primary level, proportionality and the mechanics through which it substantiates are often pervasive even at the secondary (or sub-constitutional) level as well …”
Lorenzo Dalla Corte, On proportionality in the data protection jurisprudence of the CJEU, International Data Privacy Law, https://doi.org/10.1093/idpl/ipac014. Published 21 July.